This invention relates to a natural language processing apparatus which utilizes a knowledge of linguistics to analyze the meaning of inputted written sentences comprising a natural language. More particularly, the invention relates to an apparatus for machine translation capable of translating a certain language into another language.
Systems which analyze the meaning of a natural language using a computer have been the subject of research and development in recent years.
The construction of a natural language processing apparatus according to the prior art will now be described with reference to FIGS. 1 and 2.
The conventional natural language processing apparatus shown in FIG. 1 is provided with an input sentence 301 in a natural language. An expression of meaning (or a conceptual structure) possessed by this sentence is extracted from the sentence. (Hereinafter, an expression of meaning shall be referred to as a "meaning expression".) More specifically, a morpheme analyzing unit 302 divides the input sentence 301 into morphemes, which serve as basic units, investigates the grammatical attribute (part of speech or conjugation) of each morpheme while referring to a dictionary, and assigns the checked attribute information to each morpheme. The sentence which has undergone this morpheme analysis in the morpheme analyzing unit 302 is delivered to a sentence-structure analyzing unit 303. The latter analyzes the syntactic structure of the input sentence based on the results of the morpheme analysis. That is, the unit 303 analyzes the morphemes and the dependence relationship between the morphemes and the sentence structure, and delivers the information obtained by this analysis to a meaning analyzing unit 304. The latter analyzes the meaning relationship of the input sentence from the results of analysis provided by the sentence-structure analyzing unit 303 to obtain its "meaning expression".
This "meaning expression" represents the conceptual structure of the input sentence. The results of processing performed by the language processing apparatus of the kind shown in FIG. 1 are utilized in a so-called transfer-type translating apparatus, as described in U.S. Pat. No. 5,101,349, by way of example. In order to translate one language into another language in a transfer-type translating apparatus, "meaning expressions" of the original language are converted into (transferred to) "meaning expressions" in the target language, after which a translated sentence is generated. These meaning expressions are intermediate expressions, namely expressions intermediate the input sentence and the translated sentence.
FIG. 2 illustrates the construction of the meaning analyzing unit 304 in greater detail.
The meaning analyzing unit 304 includes four analyzers connected sequentially. Specifically, when a noun-phrase range analyzer 401 accepts, as syntactic information, the results of sentence-structure analysis performed by the sentence-structure analyzing unit 303, the analyzer 401 performs analysis that is for deciding the range of a portion constituted by a noun phrase. A modification structure analyzer 402 accepts the results of this analysis and proceeds to analyze the modification structure in the text of the noun phrase. An inter-sentence meaning analyzer 403 analyzes the meaning relationship among a plurality of sentences, and a tense/aspect analyzer 404 analyzes the tense/aspect of the input sentence.
For a detailed description of the processing executed by the conventional meaning analyzing unit mentioned above, see the "Summary of the Machine Translation Project of the Science and Technology Agency" by Makoto Nagao, et. al (Information Processing, Vol. 26, No. 10, pp. 1203-1213).
The meaning analyzing unit of FIG. 2 has a plurality of analyzers which perform partial meaning analysis. This is carried out through the following sequence: analysis of noun-phrase range.fwdarw.analysis of modification structure.fwdarw.analysis of inter-sentence meaning.fwdarw.analysis of tense/aspect. A variety of other meaning analyzing units having an architecture which embraces such a plurality of analyzers have been proposed. In all of these units, meaning analyzing processing is executed in accordance with a fixed processing sequence at all times. In processing for analyzing the meaning of a natural language, the reason for performing the aforementioned partial meaning analysis in a given sequence is that the results of other specific partial analytical processing operations are required at the start of a certain analytical processing operation in order to obtain correct results.
However, the requirement in the prior-art meaning analyzing unit that the execution sequence of partial analytical processing always be fixed results in the following disadvantages.
(1) There are cases where correct analysis cannot be performed in the set sequence. The reason is that since an expression in a natural language has a complicated structure, there are instances where correct results are not obtained by following the aforementioned sequence, namely analysis of noun-phrase range.fwdarw.analysis of modification structure.fwdarw.analysis of inter-sentence meaning.fwdarw.analysis of tense/aspect, by way of example. For instance, in the example of FIG. 2, the analysis of associated structure is performed only one time, though there can be situations where this analysis must be performed twice. More specifically, for a specific phenomenon of language, there are instances where it is necessary to apply the partial analytical processor in a sequence different from that of an ordinary phenomenon of language.
(2) If it is attempted to avoid the disadvantage (1) described above while observing the rule that all processing be performed through the fixed procedure, then it will be necessary to make one processor which performs partial analytical processing bear the burden of two or more analytical processing operations. This has the effect of greatly complicating the processing of the processor which is made to bear these additional processing operations.
(3) In cases where the analytical processing added owing to (2) above becomes unnecessary or where a specific partial analytical processor must be corrected or modified, it is difficult to extract, or to revise a portion of the function of the specific partial analytical processor.